Microwave ovens
Overview A microwave oven (commonly referred to as a microwave) is a kitchen appliance that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce thermal energy in a process known as dielectric heating. Microwave ovens heat foods quickly and efficiently because excitation is fairly uniform in the outer 25–38 mm (1–1.5 inches) of a homogeneous, high water content food item; food is more evenly heated throughout (except in heterogeneous, dense objects) than generally occurs in other cooking techniques. Percy Spencer is generally credited with inventing the modern microwave oven after World War II from radar technology developed during the war. Named the "Radarange", it was first sold in 1946. Raytheon later licensed its patents for a home-use microwave oven that was first introduced by Tappan in 1955, but these units were still too large and expensive for general home use. The countertop microwave oven was first introduced in 1967 by the Amana Corporation, and their use has spread into commercial and residential kitchens around the world. In addition to their use in cooking food, types of microwave ovens are used for heating in many industrial processes. Microwave ovens are popular for reheating previously cooked foods and cooking a variety of foods. They are also useful for rapid heating of otherwise slowly prepared cooking items, such as hot butter, fats, and chocolate. Unlike conventional ovens, microwave ovens usually do not directly brown or caramelize food, since they rarely attain the necessary temperatures to produce Maillard reactions. Exceptions occur in rare cases where the oven is used to heat frying-oil and other very oily items (such as bacon), which attain far higher temperatures than that of boiling water. Microwave ovens have a limited role in professional cooking, because the boiling-range temperatures produced in especially hydrous foods impede flavors produced by the higher temperatures of frying, browning, or baking. However, additional heat sources can be added to microwave ovens, or into combination microwave ovens, to produce these other heating effects, and microwave heating may cut the overall time needed to prepare such dishes. Some modern microwave ovens are part of over-the-range units with built-in extractor hoods. History The idea of electromagnetic heating was first mentioned in the USA and both Bell Laboratories and Westinghouse thought of using it on food and patients respectively. Raytheon filed a United States patent application for Spencer's microwave cooking process in 1945 and an oven that heated food using microwave energy from a magnetron was soon placed in a Boston restaurant for testing. They launched the "Radarange", the first commercially available microwave oven, in 1947. They became popular as a labour industrial and commercial labour saving device in the mid 1960s (USA) and as a domestic appliance in the mid 1970s (USA). They then became a 'must have' item in the early 1980s (USA and UK). They were normal since the mid 1990s (USA, UK, Canada and Australia). How they work The magnetron uses electrons to generate microwaves that agitate particles in the food, heating it; and thus it cook food. Health hazards Some magnetrons have ceramic insulators with toxic beryllium oxide (beryllia) added to them. Microwaves can burn people badly. It consists of: #a high-voltage power source, commonly a simple transformer or an electronic power converter, which passes energy to the magnetron. #a high-voltage capacitor connected to the magnetron, transformer and via a diode to the chassis. #a cavity magnetron, which converts high-voltage electric energy to microwave radiation. #a magnetron control circuit (usually with a microcontroller). #a short waveguide (to couple microwave power from the magnetron into the cooking chamber). #a metal cooking chamber, with a door. #a turntable or metal wave guide stirring fan. #a digital/manual control panel. Also see *Electromagnetic spectrum Sources #https://en.wikipedia.org/wiki/Microwave_oven #http://www.newton.dep.anl.gov/askasci/chem00/chem00636.htm #http://www.smecc.org/microwave_oven.htm #http://www.inventionandtechnology.com/xml/2005/4/it_2005_4_feat_4.xml #http://www.phys.unsw.edu.au/~jw/superheating.html #http://www.animations.physics.unsw.edu.au/jw/superheating.htm #https://web.archive.org/web/20120425091608/http://emlab.uiuc.edu/ece350/suppnotes/moven.pdf #https://web.archive.org/web/20130322044917/http://www.raytheon.com/ourcompany/history/leadership/ #https://worldwide.espacenet.com/publicationDetails/biblio?CC=US&NR=2495429&KC=&FT=E&locale=en_EP #http://www.explainthatstuff.com/microwaveovens.html #http://home.howstuffworks.com/microwave.htm #https://www.universetoday.com/45527/how-do-microwaves-work/ #http://scitech.web.cern.ch/scitech/TopTech/01/MicroWaveOven/microwave_2.shtml Category:Electromagnetic spectrum Category:Food Category:Ovens